Comparative transcriptional analysis of the satellite glial cell injury response

Abstract

Satellite glial cells (SGCs) tightly surround and support primary sensory neurons in the peripheral nervous system and are increasingly recognized for their involvement in the development of neuropathic pain following nerve injury. The SGCs are difficult to investigate due to their flattened shape and tight physical connection to neurons in vivo and their rapid changes in phenotype and protein expression when cultured in vitro. Consequently, several aspects of SGC function under normal conditions as well as after a nerve injury remain to be explored. The recent advance in single cell RNAseq technologies has enabled a new approach to investigate SGCs. Here we publish a dataset from mice subjected to sciatic nerve injury as well as a dataset from dorsal root ganglia cells after 3 days in culture. We use a meta-analysis approach to compare the injury response with that in other published datasets and conclude that SGCs share a common signature following sciatic nerve crush and sciatic ligation, involving transcriptional regulation of cholesterol biosynthesis. We also observed a considerable transcriptional change when culturing SGCs, suggesting that some differentiate into a specialised in vitro state, while others start resembling Schwann cell-like precursors. The datasets are available via the Broad Institute Single Cell Portal.

The Similar and Distinct Roles of Satellite Glial Cells and Astrocytes in Neuropathic Pain

“…This is theorized to occur in order to provide greater metabolic support as neurons go through the costly process of regeneration. However, others, using flow cytometry and single cell sequencing, have found no evidence of proliferation (27,73,87). Jager and colleagues suggested that these BrdU positive cells are likely to be proliferating macrophages that have invaded the neuron-glia unit (87), a phenomenon which has been previously reported (88).…”

“…A growing body of evidence suggests that SGCs are closely related to Schwann cells and may in fact be immature Schwann cells held in their present state by interactions with sensory neurons (26). Supporting this view, SGCs rapidly change their phenotype in monoculture, becoming less broad and more closely resembling Schwann cells or their precursors, termed sympathoblasts (26,27).…”

“…However, reports of negative findings have emerged (72). RNAseq data is inconsistent, with some datasets finding little change in Gfap expression after sciatic nerve injury (27) and another identifying upregulation (73). Possible explanations include regulation of GFAP at the translational and/or protein degradation levels and alternative splicing producing isoforms not recognized by common monoclonal antibodies.…”

“…Thus, SGCs control peripheral sensitization through potassium regulation. While Kir4.1 (aka KCNJ10) is the primary Kir in rodents (186), KCNJ3 likely plays a larger role in human SGCs based on mRNA expression data (27).…”

In vivocalcium imaging shows that satellite glial cells have increased activity in painful states

“…Under a regular light microscope, SGCs are hardly visible, which has meant that their presence in peripheral neuronal culture systems often goes unnoticed (Thakur et al, 2014). On the other hand, SGCs cultured in the absence of neurons rapidly regress into a Schwann-cell like precursor phenotype (George et al, 2018;Jager et al, 2022), which means that any in vitro studies of pure SGCs have to be undertaken within 24h of extraction. Luckily, progress in optical imaging techniques has meant that SGC function can now finally be studied in vivo, using calcium imaging of dorsal root ganglia (DRG) (Chen, Huang, et al, 2022), the site of peripheral neuron-SGC units.…”